1. Field of the Invention
The present invention relates to a technology to improve the conventional wireless sensor network, particularly to a power-efficient backbone-oriented wireless sensor network, a method for constructing the same and a method for repairing the same.
2. Description of the Related Art
The wireless sensor network is mainly used to detect the values of physical parameters in the environment, such as temperature, pressure, humidity and sound, wherein many sensor nodes are arranged in the observed environment. The self-organization capability of the sensor nodes will form a wireless communication network. The sensor nodes detect specified parameters and transmit the detection results to the sink or the data collector via the wireless communication network. The detection results are processed and analyzed, and then appropriate responses are made. As a wireless sensor network can operate without manual operation or manual administration, it has been widely used in many fields, such as military detection, healthcare, environmental surveillance, and home security. The IEEE802.15.4 standard in TG4 of IEEE802.15 features low rate, low power consumption and low cost, and thus quite meets the requirements of a wireless sensor network. Therefore, IEEE802.15.4 has been one of the protocols adopted by wireless sensor networks.
In the researches of wireless sensor networks, power consumption is always a hot topic. In a sensor network, each sensor node transmits the collected data to the server. However, numerous sensor nodes are distributed in the environment respectively with different distances to the server. Thus, not all the sensor nodes are able to directly connect with the server. The sensor nodes distant from the server rely on the sensor nodes near the server to pass their data to the server. Therefore, the nearer a sensor node is to the server, the heavier the burden the sensor node bears. A sensor node usually has limited power storage. When energy is used up, the posterior sensor nodes cannot send their data to the server. Thus, the sensor network malfunctions. Refer to FIG. 1. Nodes A, B and C are three sensor nodes 12 nearest to a server 10. Nodes A, B and C not only have to transmit their own data but also have to transmit data for the posterior sensor nodes 12. Therefore, Nodes A, B and C have loads heavier than the other sensor nodes 12. Thus, Nodes A, B and C consume energy in a higher rate. When Node A, B or C exhausts the energy thereof, the posterior sensor nodes 12 cannot send their data to the server 12. As a result, the sensor network malfunctions. In such a case, Node A, B or C becomes the so-called hot spot. Although the sensor nodes 12 posterior to the hot spot still have electric energy, they cannot transmit the data to the server 12. Therefore, the hot-spot problem will decrease the operation duration of the sensor network.
Accordingly, the present invention proposes a power-efficient backbone-oriented wireless sensor network, a method for constructing the same and a method for repairing the same to decrease the hot spots and prolong the operation duration. The architecture and embodiments of the present invention will be described in detail below.